High-density tungsten-rhenium-nickel alloys and articles

ABSTRACT

Sintered alloys of tungsten containing between about 1 percent and 7.5 percent rhenium and between about 0.15 percent and 0.3 percent nickel and electrical articles, particularly contacts, prepared from said alloys. The invention also includes a method of improving the density of tungsten alloys.

United States Patent [151 3,638,293 Peterson [4 Feb. 1, 1972 [54]HIGH-DENSITY TUNGSTEN-RHENIUM- 2,227,445 l/l94l Driggs.... ..75/200NICKEL ALLOYS AND ARTICLES 2,466,992 4/1949 Kurtz ..75/ 176 3,359,08212/1967 Dickinson ..29/182 [72] Inventor: Sven Torsten Lennart Peterson,Vendelso,

Sweden [73] Assignee: Lumalampan Aktiebolag, Stockholm,

Sweden [22] Filed: Sept. 12, 1969 I 211 App]. No: 857,478

[52] US. Cl ..29/l82, 75/176, 75/221, 252/515 [51] Int. Cl. ..B22i 3/00[58] Field of Search ..29/182; 75/176; 252/515 [56] References CitedUNITED STATES PATENTS 2,157,935 5/1939 Hensel ..75/l76 DENSITY a/cc.

Primary Examiner-Carl D. Quarforth Assistant Examiner-R. E. SchaferAttorney-Herbert H. Goodman [5 7] ABSTRACT 'Sintered alloys of tungstencontaining between about l'per 14 Claims, 3 Drawing Figures 0.20% NICKELWEIGHT PERCENT RHENIUM PATENTEDFEBI 1972 3633.293

SHEET 1 OF 2 0.20% NICKEL DENSITY s/cc.

OI23456789IO WEIGHT PERCENT RHENIUM INVENTOR SVEN TORSTEN LENNARTPETERSON BY (5W 9 ATTORNEYS HIGH-DENSITY TUNGSTEN-RIIENIUM-NICKEL ALLOYSAND ARTICLES BACKGROUND OF THE INVENTION Tungsten is widely used inindustry for electrical materials such as contacts. The most widely usedmethod for manufacturing tungsten articles is the powder metallurgicmethod. This conventionally involves preparation of the metal powder (ormixture of metal powders when alloys are to be prepared), reduction,pressing, presintering, and then sintering to obtain a relatively densearticle. Presintering and sintering are carried out in an inert orreducing atmosphere. This is usually followed by working, i.e., coldworking or hot working, such as pressing, rolling, swaging, etc., toincrease density. The sequence of operations depends upon the specificarticle being manufactured and the properties and characteristicsdesired. These include electrical and tensile properties,recrystallization characteristics, grain size and orientation, porosity,nonmetallic inclusions, density, purity, etc.

It is a major advantage to obtain an article in the as sinteredcondition having the greatest possible density. This eliminates furtherworking such as swaging. The advantages that follow are lower costs andminimized effect upon the recrystallization properties. It is alsoadvantageous to obtain maximum density or the desired density at lowersintering temperatures, and particularly temperatures not higher thanabout 1,500-1,600 C. This results in lower cost and the ability toutilize conventional sintering furnaces. It also avoids the undesirableeffects upon the electrical and/or metallographic characteristics thatsometime result from extremely high temperature sintering.

The present invention provides high density tungsten-rhenium-nickelalloys and articles made therefrom.

BRIEF SUMMARY OF INVENTION Sintered high-density alloy compositionscontaining between about 1 and 7.5 percent rhenium and between about0.15 and 0.3 percent nickel, and electric contacts prepared therefrom.

The preferred compositions have a density of at least 18.6 g./cc. andmore preferably, a density of at least 19 g./cc.

Within the range of alloys disclosed and of electrical contact alloycompositions, preferred compositions include the following: Between 2and 7 percent rhenium and between 0.2 and 0.3 percent nickel; between 1and 7.5 percent rhenium and 0.3 percent nickel; between 2 and 5.5percent rhenium and 0.2 and 0.3 percent nickel; and about 3 percentrhenium and 0.15 percent nickel.

The following compositions are also useful, although not as preferred asthose listed in the preceding paragraph: Between 1 and 5.5 percentrhenium and 0.15 and 0.3 percent nickel; and between 2 and 4 percentrhenium and 0.15 percent nickel.

BRIEF DESCRIPTION OF DRAWINGS FIG, 1 is a graph relating alloycompositions to the density as sintered for the conditions andcompositions in the examples herein;

FIG. 2 is a photomicrograph, 100 x, of an unetched section of the assintered alloy composition containing 0.2 percent nickel, 3 percentrhenium and the remainder tungsten; and

FIG. 3 is a photomicrograph, 425 x, of an etched section of the samealloy.

DETAILED DESCRIPTION OF INVENTION The tungsten alloy articles of thepresent invention are manufactured by conventional powder metallurgictechniques. The alloy powder mixture may be prepared by admixing powdersof nickel, rhenium and tungsten. They are preferably prepared byadmixing reducible metal compounds of each of the metals. Nickel ispreferably added as nickel carbonate or nickel oxide. Rhenium ispreferably added as ammonium perrhenate. Tungsten is preferably added astungstic oxide. Mixing is preferably carried out in a ball mill having aliquid medium, e.g., alcohol, methylene chloride, etc. After mixing hasbeen carried out until a homogeneous mixture is attained, the mixture isremoved from the ball mill, dried and reduced in hydrogen, preferably ata temperature of between about 700 and l,000 C. The resultant mixedmetal powders are preferably treated by addition of a hydrocarbonmaterial such as paraffin wax in a solvent to improve compactability. Agreen compact is then formed by pressing, preferably at a pressure ofabout 15 tons per square inch. The green compact is then presintered,preferably at a temperature of about 800 to 1,000 C. for a period ofabout one-half hour. Sintering is then carried out at elevatedtemperatures. The preferred sin tering temperature, utilizing the alloycompositions of the present invention, is between about 1,400 and 1,550C. Sintering time is preferably between about 1 and 3 hours. Thisrelatively low temperature sintering provides the desired densitywithout at the same time reaching sufficiently high temperatures toundesirably affect physical and metallographic properties. Presinteringand sintering are carried out in a protective atmosphere, i.e., vacuum,an inert atmosphere or a reducing atmosphere. The sintered articles maythen be finished by tumbling or lapping, or, if necessary, finishmachined to the desired dimensions.

The invention is further illustrated in the following examples. Allparts and percentages specified in this application are by weight unlessotherwise specified. a

The tungsten alloy articles of all the examples were prepared using thesame procedure. A mixture of tungstic oxide, ammonium perrhenate, andnickel carbonate was thoroughly mixed in a ball mill containing ethylalcohol. The mixed powder was then reduced in hydrogen at a temperatureof between about 700 and 1,000 C. The mixed powders were then treatedwith a solution of paraffin wax in benzene in the conventional manner.Green compacts were formed at 15 tons per square inch pressure. Thegreen compacts were then presintered at a temperature of between about800 and l,000 C. for one-half hour in a hydrogen atmosphere (dewpoint 60F.) and were then sintered in a hydrogen atmosphere (dewpoint 60 F.) ata temperature of 1,500" C. for 1 hour. During sintering, there was ashrinkage of about 45 percent by volume of the tungsten-rhenium-nickelalloys. The metal articles produced from these alloys have unusuallyhigh density, are coherent, and have a homogeneous structure, as shownin FIG. 2, a photomicrograph x) of an unetched section, and FIG. 3, aphotomicrograph (425 x) of an etched section of the alloy composition0.20 percent nickel and 3 percent rhenium.

The density of various tungsten-rhenium-nickel sintered articles isreported in table I, together with the densities of a number ofdifferent tungsten alloys (and also unalloyed tungsten) for comparativepurposes.

and 7 percent rhenium and between about 0.2 and 0.3 percent nickel andhaving a density as sintered in excess of 19 g./cc.

3. The compositions of claim 1 containing about 0.3 percent nickel andhaving a density as sintered in excess of 19 g./cc.

4. The compositions of claim 1 containing between about 1 and 5.5percent rhenium.

5. The compositions of claim 4 containing at least about 2 percentrhenium and containing at least about 0.2 percent nickel and having adensity as sintered in excess of 19 g./cc.

6. The compositions of claim 4 containing between about 2 and 4 percentrhenium and containing about 0.15 percent nickel.

7. The compositions of claim 6 containing about 3 percent rhenium andhaving a density as sintered in excess of 19 g./cc.

8. Sintered high-density electric contacts consisting essentially ofbetween about I and 7.5 percent rhenium, between about 0.15 and 0.3percent nickel and the balance tungsten.

9. The electric contacts of claim 8 containing between about 2 and 7percent rhenium and between about 0.2 and 0.3 percent nickel, and havinga density in excess of IQ g./cc.

10. The electric contacts of claim 8 containing about 0.3 percent nickeland having a density in excess of l9 g./cc.

11. The electric contacts of claim 8 containing between 1 and 5.5percent rhenium.

12. The electric contacts of claim 11 containing at least 2 percentrhenium and containing at least 0.2 percent nickel and having a densityin excess of 19 g./cc.

13. The electric contacts of claim 11 containingbetween 2 andfl percentrhenium and containing about 0.l5 percent nickel.

14. The electric contacts of claim 13 containing about 3 percent rheniumand having a density in excess of 19 g./cc.

2. The compositions of claim 1 containing between about 2 and 7 percentrhenium and between about 0.2 and 0.3 percent nickel and having adensity as sintered in excess of 19 g./cc.
 3. The compositions of claim1 containing about 0.3 percent nickel and having a density as sinteredin excess of 19 g./cc.
 4. The compositions of claim 1 containing betweenabout 1 and 5.5 percent rhenium.
 5. The compositions of claim 4containing at least about 2 percent rhenium and containing at leastabout 0.2 percent nickel and having a density as sintered in excess of19 g./cc.
 6. The compositions of claim 4 containing between about 2 and4 percent rhenium and containing about 0.15 percent nickel.
 7. Thecompositions of claim 6 containing about 3 percent rhenium and having adensity as sintered in excess of 19 g./cc.
 8. Sintered high-densityelectric contacts consisting essentially of between about 1 and 7.5percent rhenium, between about 0.15 and 0.3 percent nickel and thebalance tungsten.
 9. The electric contacts of claim 8 containing betweenabout 2 and 7 percent rhenium and between about 0.2 and 0.3 percentnickel, and having a density in excess of 19 g./cc.
 10. The electriccontacts of claim 8 containing about 0.3 percent nickel and having adensity in excess of 19 g./cc.
 11. The electric contacts of claim 8containing between 1 and 5.5 percent rhenium.
 12. The electric contactsof claim 11 containing at least 2 percent rhenium and containing atleast 0.2 percent nickel and having a density in excess of 19 g./cc. 13.The electric contacts of claim 11 containing between 2 and 4 percentrhenium and containing about 0.15 percent nickel.
 14. The electriccontacts of claim 13 containing about 3 percent rhenium and having adensity in excess of 19 g./cc.